JP2011241567A - Bolt looseness detection system, bolt looseness detection device, and bolt management implement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bolt looseness detection system for correctly and efficiently detecting bolt looseness with a simple structure.SOLUTION: An RFID tag 11 is mounted on the head of a bolt 20. The RFID tag 11 and the bolt 20 are covered with a radio shielding cover 12. Among response waves transmitted from the RFID tag 11, the ones passing through a slit 13 provided on the radio shielding cover 12 are received by an RFID reader/writer. Because the intensity of a radio waves passing through the slit 13 changes corresponding to the looseness angle of the bolt 20, the looseness of the bolt 20 is detected based on whether the ID information included in the response waves is readable or not and the received electric field intensity.

Description

  The present invention relates to a system for detecting loose bolts using a Radio Frequency Identification (hereinafter referred to as RFID) system.

  The RFID system is a system that performs wireless communication between an RFID tag including an IC chip and an RFID reader / writer. There are two types of RFID tags: an active type tag that is equipped with a battery and is driven by the electric power, and a passive type tag that is driven by receiving electric power from the RFID reader / writer and using it as a power source. Since the active type has a battery compared to the passive type, it has advantages such as communication distance and communication stability, but it also has disadvantages such as complicated structure, larger size, and higher cost.

  With recent improvements in semiconductor technology, IC tags for passive tags have become smaller and higher in performance, and the use of passive tags in a wide range of fields is expected. In the passive tag, an electromagnetic induction method is applied when the frequency band is a long wave band or a short wave band. In the electromagnetic induction method, a voltage is induced in the RFID tag by electromagnetic induction between the transmission antenna coil of the RFID reader / writer and the antenna coil of the RFID tag, and the IC chip is activated by this voltage to enable communication. Therefore, the RFID tag operates only within the induction electromagnetic field by the RFID reader / writer, and the communication distance is limited to about several tens of centimeters.

  On the other hand, a radio wave communication method is applied to an RFID tag in a high frequency band such as a UHF band or a microwave band. Since electric power is supplied to the IC chip of the RFID tag by radio waves, the communication distance is greatly improved to about 1 to 7 m. Therefore, it is possible to perform communication during movement, which has been difficult to realize with long-wave band and short-wave band RFID systems with a short communication distance, and the range of use is expected to be greatly expanded.

  Many bolts are used for machinery and equipment, and a method for managing the fastening state of the bolts using an RFID system has been proposed. In the conventional bolt management tool, a switch arranged in the vicinity of the bolt is switched between closing and opening according to the fastening state of the bolt, and the RFID tag responds according to the state of this switch. The switch has a structure that closes when the bolt is normally fastened and opens when the bolt is loosened. The looseness of the bolt is detected by reading response information from the RFID tag provided in the bolt management tool with an RFID reader / writer (for example, refer to Patent Document 1).

  For example, in the railway field, there is a demand for simplifying the maintenance of ground facilities. In the ground equipment in the railway field, a plurality of bolts are used to fix rails for railroads (hereinafter referred to as rails) to sleepers. In order to detect looseness of these bolts, the above bolt management tool is used. It has been proposed to do. By installing a bolt management tool in the vicinity of the bolt for fixing the rail to the sleeper, and placing an RFID reader / writer on the train traveling on the rail, the RFID reader / writer and the RFID tag of the bolt management tool while the train is running And loosening of the bolt is detected (for example, see Patent Document 2).

JP 2009-066667 A JP 2009-064111 A

  The conventional bolt management tool requires a mechanical switch that switches between closing and opening according to the fastening state of the bolt, and the structure is complicated because the switch, the bolt, and the RFID tag must be connected. When a switch used for the bolt management tool fails, there is a problem that the bolt loosening detection system cannot accurately detect the bolt loosening. For this reason, it is necessary to maintain the bolt management tool itself. As a result, there is a problem that maintenance of machinery and equipment cannot be simplified and feasibility and operability are low. In particular, in the railway field, there is a demand for simplifying the maintenance of the ground equipment, but since the maintenance of the bolt management tool itself including a mechanical switch is required, the maintenance of the ground equipment cannot be simplified.

  The present invention has been made in order to solve the above-described problems. A bolt looseness detection system capable of accurately and efficiently detecting bolt looseness with a simple structure, a bolt looseness detection device constituting the bolt loosening detection system, and the like The purpose is to obtain a bolt management tool.

  The bolt loosening detection system according to the present invention includes a bolt management tool having an RFID tag fixed to a bolt and a radio wave shielding cover provided with a slit, and an antenna unit that receives a radio wave radiated from the RFID tag and passed through the slit. And a loosening detection of a bolt having an RFID reader / writer that demodulates the radio wave received by the antenna unit and reads the ID information of the RFID tag, and a detection unit that detects the looseness of the bolt based on whether or not the ID information of the RFID tag can be read And a device.

  A bolt loosening detection device according to the present invention includes an antenna unit that receives radio waves radiated from an RFID tag covered by a radio wave shielding cover having slits and that has passed through the slits, and demodulates radio waves received by the antenna unit, and the RFID tag An RFID reader / writer that reads the ID information of the RFID tag, and a detection unit that detects looseness of the bolt based on whether or not the ID information of the RFID tag can be read.

  A bolt management tool according to the present invention includes an RFID tag fixed to a bolt, and a radio wave shielding cover provided with a slit and covering the bolt and the RFID tag.

  The present invention utilizes the fact that the strength of the radio wave passing through the slit of the radio wave shielding cover changes due to the loosening of the bolt, and notifies the bolt loosening detection device from the bolt management tool to the bolt loosening detection device. Bolt management tools can be realized with a simple structure called a cover, and bolt looseness can be detected accurately and efficiently.

It is explanatory drawing which shows the volt | bolt loosening detection system in Embodiment 1 of this invention. It is an enlarged view which shows the X section of FIG. It is a perspective view which shows the volt | bolt management tool in Embodiment 1 of this invention. It is sectional drawing which shows the volt | bolt management tool in Embodiment 1 of this invention. It is a block diagram which shows the bolt loosening detection apparatus in Embodiment 1 of this invention. It is a perspective view which shows the antenna part and bolt management tool in Embodiment 1 of this invention. It is a flowchart which shows operation | movement of the volt | bolt loosening detection apparatus in Embodiment 1 of this invention. It is a block diagram which shows the bolt loosening detection apparatus in Embodiment 2 of this invention. It is a block diagram which shows the antenna control part in Embodiment 2 of this invention. It is a functional block diagram which shows the antenna control part in Embodiment 2 of this invention. It is a radiation pattern figure of the antenna part in Embodiment 2 of this invention. It is a functional block diagram which shows the antenna control part in Embodiment 2 of this invention. It is a radiation pattern figure of the antenna part in Embodiment 2 of this invention. It is a radiation pattern figure of the antenna part in Embodiment 2 of this invention. It is a flowchart which shows operation | movement of the bolt loosening detection apparatus in Embodiment 2 of this invention. It is a radiation pattern figure of the antenna part in Embodiment 2 of this invention. It is a flowchart which shows operation | movement of the bolt loosening detection apparatus in Embodiment 2 of this invention.

  Embodiments according to the present invention will be described with reference to the drawings. In the following drawings, the same reference numerals indicate the same or corresponding configurations. In the following embodiments, the case where the present invention is used in the railway field will be described. However, the present invention is not limited to the embodiments described below.

Embodiment 1 FIG.
FIG. 1 is an explanatory diagram showing a bolt loosening detection system according to Embodiment 1 of the present invention. FIG. 2 is an enlarged view showing a portion X in FIG. FIG. 3 is a perspective view showing the bolt management tool according to Embodiment 1 of the present invention. 2 and FIG. 3 are perspective views of a radio wave shielding cover 12 described later in order to show the internal structure of the bolt management tool. FIG. 4 is a cross-sectional view showing the bolt management tool according to Embodiment 1 of the present invention. FIG. 5 is a configuration diagram illustrating the bolt loosening detection device according to the first embodiment of the present invention. Hereinafter, the configuration of the bolt loosening detection system will be described with reference to FIGS. 1 to 5.

  The bolt looseness detection system includes a bolt looseness detection device 1 and a bolt management tool 10. When detecting the looseness of the bolt 20 which is a fixing tool for fixing the rail to the sleepers using the bolt loosening detection system of the present embodiment, a train traveling on the rail (a railroad including a test vehicle or the like) The bolt looseness detection device 1 is installed on the entire vehicle (not shown in FIGS. 1 and 2), and the bolt management tool 10 is installed in the vicinity of the bolt 20.

  The bolt management tool 10 includes a passive RFID tag 11 attached to the head of a bolt 20 for fixing a rail to a sleeper, and a radio wave shielding cover 12 that covers the RFID tag 11 and the bolt 20. The radio wave shielding cover 12 is made of a material that shields radio waves and has a slit 13.

  The RFID tag 11 may be fixed to the head of the bolt 20 with an adhesive or the like (see FIG. 3), or fixed using a bolt cap 14 for covering the head of the bolt 20 as shown in FIG. May be. By putting the bolt cap 14 including the RFID tag 11 on the head of the bolt 20, the RFID tag 11 can be easily fixed to the head of the bolt 20, and the efficiency of the work of fixing the RFID tag 11 to the bolt 20 is increased. Further, if the bolt cap 14 larger than the head of the bolt 20 is formed of a thermosetting resin, the RFID tag 11 can be freely oriented in a desired direction when the bolt cap 14 is put on the head of the bolt 20. After the orientation of the bolt cap 14 is determined, the bolt cap 14 can be thermoset and placed on the head of the bolt 20.

  As shown in FIG. 5, the bolt loosening detection device 1 includes an antenna unit 2, an RFID reader / writer unit 3, and a detection unit 4. The RFID reader / writer 3 performs wireless communication with the RFID tag 11 of the bolt management tool 10 via the antenna unit 2, and the detection unit 4 detects looseness of the bolt 20 based on input data from the RFID reader / writer 3. To do.

  The interrogation wave from the RFID reader / writer 3 to the RFID tag 11 and the response wave from the RFID tag 11 to the RFID reader / writer 3 are transmitted through the slit 13 of the radio wave shielding cover 12. The RFID tag 11 that has received the interrogation wave from the RFID reader / writer 3 returns a response wave to which the unique ID information is added to the RFID reader / writer 3. The RFID reader / writer 3 that has demodulated the response wave received by the antenna unit 2 outputs the unique ID information, received electric field strength, time information, and the like transmitted from the RFID tag 11 to the detection unit 4. The detection unit 4 detects looseness of the bolt 20 using data output from the RFID reader / writer 3.

  Instead of the detection unit 4, a storage unit that stores data output from the RFID reader / writer 3 may be provided. For example, if the recording unit is composed of a recording medium that can be taken out, the detection unit 4 is not directly connected to the RFID reader / writer 3 and is not physically connected to the recording medium. The looseness of the bolt 20 can be detected by the detection unit 4 accessing.

  FIG. 6 is a perspective view showing the antenna unit and the bolt management tool according to Embodiment 1 of the present invention. FIG. 6A is a perspective view of a normal state where the bolt is not loosened, and FIG. 6B is a perspective view of a state where the bolt is loosened. The principle of detecting loosening of the bolt 20 will be described with reference to FIG. FIG. 6 is a perspective view of the radio wave shielding cover 12 in order to explain the internal structure of the bolt management tool 10.

  The radio wave (interrogation wave) emitted from the antenna unit 2 of the bolt looseness detection device 1 passes through the slit 13 of the radio wave shielding cover 12 and reaches the RFID tag 11 disposed inside the radio wave shielding cover 12. The RFID tag 11 supplied with power by the radio wave from the bolt loosening detection device 1 emits a response wave to which unique ID information is added.

  A case will be described in which the bolt 20 to which the RFID tag 11 is attached has changed from the normal state shown in FIG. 6A to the state shown in FIG. Since the RFID tag 11 is fixed to the head of the bolt 20, the relative angle of the RFID tag 11 with respect to the slit 13 changes according to the loosening angle of the bolt 20. As the relative angle changes, the intensity of the radio wave passing through the slit 13 also changes. For example, in the positional relationship between the RFID tag 11 and the slit 13 shown in FIG. 6A, the intensity of the radio wave passing through the slit 13 is maximum (that is, the intensity of the radio wave shielded by the radio wave shielding cover 12 is minimum). Shall. On the other hand, in the positional relationship between the RFID tag 11 and the slit 13 shown in FIG. 6B, the relative angle of the RFID tag 11 to the slit 13 is different from the state shown in FIG. Compared with the state shown in FIG. 2, the intensity of the radio wave passing through the slit 13 decreases (that is, the intensity of the radio wave shielded by the radio wave shielding cover 12 increases).

  When the bolt 20 shown in FIG. 6A is normally tightened, the RFID reader 11 can read the ID information of the RFID tag 11. On the other hand, in the state where the bolt 20 shown in FIG. 6B is loose, the intensity of the radio wave shielded by the radio wave shielding cover 12 is increased as compared with the state shown in FIG. Reading of the RFID tag 11 becomes impossible. Alternatively, even if the RFID tag 11 can be read, the received electric field strength at the RFID reader / writer 3 is reduced as compared with a normal state. That is, before and after the loosening of the bolt 20, the readability state of the ID information of the RFID tag 11 changes, or the received electric field strength at the RFID reader / writer 3 changes even if the readability state does not change. Using this state change, the looseness of the bolt 20 is detected. The looseness of the bolt 20 is detected based on whether or not the ID information of the RFID tag 11 can be read, or based on the readability and the received electric field strength.

  Hereinafter, the operation of the bolt loosening detection system will be described. FIG. 7 is a flowchart showing the operation of the bolt loosening detection apparatus according to Embodiment 1 of the present invention. In step S 10, the RFID reader / writer 3 demodulates the response wave from the RFID tag 11 and reads the ID information of the RFID tag 11. Next, the RFID reader / writer 3 determines whether or not the ID information of the RFID tag 11 has been read (step S20).

  In step S20, if the ID information cannot be read, it is determined whether or not the process proceeds to step S60 and the process ends. If the ID information is continued, the process returns to step S10 and the ID information of the RFID tag 11 is read again. On the other hand, when the ID information can be read in step S20, the detection unit 4 determines whether or not the ID information is overflowed (step S30). For example, if ID information is set by serial numbers for adjacent bolts 20, the ID information of the newly read bolt 20 is the previous bolt 20 (the bolt installed next to the newly read bolt 20. It may be determined whether or not the ID information and the serial number of 20). When the train is stopped, it is conceivable to continuously read the ID information of the RFID tags 11 installed on the same bolt 20. For this reason, even if the ID information is the same instead of the serial number, it is determined that there is no overflow of the ID information if there is no skipping of the number.

  If it is determined in step S30 that there is an overreading of ID information, the process proceeds to step S35, where the overread ID information is extracted and recorded. On the other hand, if it is determined in step S30 that there is no overflow of the ID information, it is determined whether the received electric field intensity of the response wave from the RFID tag 11 is appropriate (step S40). Regarding the suitability of the received electric field strength, for example, a predetermined threshold value is compared with the received electric field strength, and it is determined that the received electric field strength is appropriate if the received electric field strength is higher than the predetermined threshold value. Alternatively, if the difference between the received electric field strength acquired at the previous bolt looseness detection and the newly acquired received electric field strength is larger than a predetermined determination value in the same ID information, it is determined to be inappropriate.

  In step S40, if it is determined that the received electric field strength of the response wave is not appropriate, the process proceeds to step S45, and the fact that the received electric field strength is abnormal is recorded. On the other hand, if it is determined in step S40 that the received electric field strength of the response wave is appropriate, the reading result of the ID information is stored (step S50). For example, ID information, received electric field strength, time, and the like can be considered as a result of reading ID information. In step S60, it is determined whether or not the bolt loosening detection is to be ended.

  As described in the principle of bolt loosening detection described above, when the bolt 20 is loosened, the relative angle of the RFID tag 11 with respect to the slit 13 changes, and the intensity of the radio wave passing through the slit 13 changes. For this reason, although the ID information was initially read by the RFID reader / writer 3 (at the time of bolt tightening), the ID information of the RFID tag 11 fixed to the loose bolt 20 cannot be read. It is judged that it is overflowing. Even if the bolt 20 is not readable, the strength of the radio wave shielded by the slit 13 increases when the bolt 20 is loosened. Therefore, the received electric field strength of the response wave received by the RFID reader / writer 3 is reduced, and in step S40 It is determined that the received electric field strength is not appropriate. In step S35, the overread ID information is recorded, and even when the received electric field strength is not appropriate, the ID information is recorded in step S45. Therefore, it is possible to detect that the bolt 20 corresponding to the ID information is loose. The looseness of the bolt 20 may be detected based only on whether the ID information can be read, or the looseness of the bolt 20 may be detected based on the received electric field strength in addition to whether the ID information can be read.

  Since the relative angle of the RFID tag 11 with respect to the slit 13 of the radio wave shielding cover 12 changes due to the loosening of the bolt 20 and the intensity of the radio wave passing through the slit 13 changes, the loosening of the bolt 20 is notified. The bolt management tool 10 according to the first embodiment can be realized with a simple configuration of the RFID tag 11 and the radio wave shielding cover 12.

  The bolt looseness detection system according to the first embodiment is based on the ID information of the RFID tag 11 obtained from the response wave that has passed through the slit 13 of the bolt management tool 10 or based on the ID information and the received electric field strength. 1, the looseness of the bolt 20 is detected, so the looseness of the bolt 20 can be detected accurately and efficiently.

Embodiment 2. FIG.
When installing a bolt looseness detection device on something that moves at a high speed like a train, it communicates with multiple RFID tags at once, and it is not the RFID tag of the target bolt, but the RFID installed on the adjacent bolt There is a risk of reading tag ID information. In order to communicate only with the RFID tag to be identified, the beam width of the antenna unit may be narrowed. However, in order to reduce the beam width of the antenna part, the shape of the antenna part must be increased, which is not practical. In the second embodiment, the antenna unit 2 includes a plurality of element antennas, and the antenna unit 2 is beam-controlled from the antenna control unit 5.

  Hereinafter, differences from the bolt loosening detection system according to the first embodiment will be described. FIG. 8 is a configuration diagram showing the bolt loosening detection device 1 according to Embodiment 2 of the present invention. The antenna unit 2 includes a first element antenna 2a and a second element antenna 2b. The antenna control unit 5 performs beam control of the antenna unit 2 based on a control signal from the RFID reader / writer 3.

  FIG. 9 is a configuration diagram showing the antenna control unit 5 according to Embodiment 2 of the present invention. An S1 switch 50 a that is a switch circuit in the antenna control unit 5 is connected to the RFID reader / writer 3. The S1 switch 50a is connected to the S2 switch 50b which is a switch circuit (P1-PC). The S2 switch 50b is connected to the S3 switch 50c, which is a switch circuit, and a hybrid coupler (180 °) 51 (P1-P2, P2-PC). In addition to the connection (P1-P2) with the S2 switch 50b, the S3 switch 30c is also connected to the hybrid coupler (180 °) 51 (P1-PC).

  The S1 switch 50a is also connected to an S4 switch 50d that is a switch circuit (P2-PC). The S4 switch 50d is connected to the S5 switch 50e, which is a switch circuit, and a hybrid coupler (180 °) 51 (P1-P2, P1-PC). In addition to the connection (P1-P2) with the S4 switch 50d, the S5 switch 50e is also connected with a hybrid coupler (180 °) 51 (P2-PC). Note that P1, P2, and PC are names of ports (terminals) of each switch circuit and the hybrid coupler (180 °) 51, and the port of the hybrid coupler (180 °) 51 is 4 for simplicity of explanation. Although all the terminals are “PC”, the actual connection relationship is as shown in FIG. 9, and it goes without saying that they are different ports.

  Since the antenna control unit 5 adopts such a configuration, the antenna control unit 5 is changed by changing the connections of the S1 switch 50a, S2 switch 50b, S3 switch 50c, S4 switch 50d, and S5 switch 50e, which are switch circuits. Can perform beam control on the antenna unit 2. The connection control of each switch circuit is performed based on a control signal supplied from the RFID reader / writer 3. That is, it can be said that the RFID reader / writer 3 performs beam control on the antenna unit 2 via the antenna control unit 5.

  Next, beam control of the antenna unit 2 will be described with reference to FIGS. In FIG. 10 and subsequent figures, there are a plurality of diagrams showing the connection state of the antenna control unit 5 described in FIG. 9. In these figures, the portions that are not connected are schematically shown with the wiring omitted. Further, in FIG. 11 and subsequent figures, there are a plurality of diagrams showing the radiation patterns. X [m] on the vertical axis indicates the size of the radiation pattern along the antenna surface of the antenna unit 2, and Z [m] on the horizontal axis. Indicates the size of the radiation pattern directed to the front of the antenna surface of the antenna unit 2.

  FIG. 10 is a functional block diagram showing the antenna control unit 5 according to Embodiment 2 of the present invention. FIG. 11 is a radiation pattern diagram of the antenna unit 2 according to Embodiment 2 of the present invention. A radiation pattern 31 shown in FIG. 11 is a radiation pattern when the first element antenna 2a and the second element antenna 2b are synthesized in the same phase. As shown in FIG. 10, the switch circuit and the hybrid coupler 51 in the antenna control unit 5 are switched by the control signal from the RFID reader / writer 3, and S1 switch 50a-S2 switch 50b-hybrid coupler 51-S3 switch. 50c-first element antenna 2a, S1 switch 50a-S2 switch 50b-hybrid coupler 51-S5 switch 50e-second element antenna 2b. The first element antenna 2 a and the second element antenna 2 b are combined in phase by the hybrid coupler 51.

  In addition, the radiation pattern 32 at the time of using only the 1st element antenna 2a is shown with a broken line in FIG. Comparing the radiation pattern 32 and the radiation pattern 31, it can be seen that the beam width of the radiation pattern 31 is narrow. By combining the first element antenna 2a and the second element antenna 2b with the same phase by the antenna control unit 5, the beam width of the antenna unit 2 can be narrowed.

  When the RFID tags 11a to 11c are arranged as shown in FIG. 11, the radiation pattern 31 synthesized in the same phase can communicate with the RFID tag 11a, but the RFID tag arranged on both sides of the RFID tag 11a. 11b and 11c cannot communicate with each other, and can communicate only with the RFID tag 11a to be identified. When only the first element antenna 2a is used, the radiation pattern is 32, so that communication with a plurality of RFID tags 11a and 11b becomes possible. If the first and second element antennas 2a and 2b are combined in the same phase, the beam width can be narrowed, and communication is performed only with the RFID tag 11a to be identified, so there is no false detection of nearby RFID tags 11b and 11c. , Bolt looseness can be detected more accurately.

  FIG. 12 is a functional block diagram showing the antenna control unit 5 according to Embodiment 2 of the present invention. FIG. 13 is a radiation pattern diagram of the antenna unit 2 according to Embodiment 2 of the present invention. A radiation pattern 33 shown in FIG. 13 is a radiation pattern when the first element antenna 2a and the second element antenna 2b are synthesized in opposite phases.

  As shown in FIG. 12, the switch circuit and the hybrid coupler 51 in the antenna control unit 5 are switched by the control signal from the RFID reader / writer 3, and S1 switch 50a-S4 switch 50d-hybrid coupler 51-S3 switch. 50c-first element antenna 2a, S1 switch 50a-S4 switch 50d-hybrid coupler 51-S5 switch 50e-second element antenna 2b. The first element antenna 2 a and the second element antenna 2 b are combined in antiphase by the hybrid coupler 51.

  By using the radiation pattern 31 obtained by synthesizing the first and second element antennas 2a and 2b in the same phase and the radiation pattern 33 synthesized in the opposite phase, the detection area of the RFID tag can be narrowed. FIG. 14 is a radiation pattern diagram of the antenna unit 1 according to Embodiment 2 of the present invention. FIG. 15 is a flowchart showing the operation of the bolt loosening detection apparatus according to the second embodiment of the present invention, and shows details of the ID information reading operation in step S10 shown in FIG.

  First, each switch of the antenna control unit 5 and the hybrid coupler 51 are switched by a control signal from the RFID reader / writer 3 to radiate radio waves with a radiation pattern 31 in which the first and second element antennas 2a and 2b are synthesized in the same phase. Then (step S11), the response wave from the RFID tag is demodulated to obtain ID information (step S12). Here, ID information of the RFID tags 11a and 11b existing in the region of the radiation pattern 31 is acquired.

  Next, each switch of the antenna control unit 5 and the hybrid coupler 51 are switched by a control signal from the RFID reader / writer 3, and radio waves are transmitted with a radiation pattern 33 obtained by synthesizing the first and second element antennas 2a and 2b in opposite phases. Radiate (step S13) and demodulate the response wave from the RFID tag to obtain ID information (step S14). Here, ID information of the RFID tags 11b, 11c and 11d existing in the region of the radiation pattern 33 is acquired.

  The RFID tag included in the detection area 34 (hatched portion shown in FIG. 14) is recognized as an identification target, and the ID information is read (step S15). That is, the RFID tag 11a detected by the radiation pattern 31 and not detected by the radiation pattern 33 becomes an identification target. For example, since the RFID tag 11b is detected by both the radiation patterns 31 and 33, it is not an identification target. The detection area 34 is obtained by subtracting the radiation pattern 33 from the radiation pattern 31, and is a narrower area than the radiation pattern 31.

  In addition, the detection area of the RFID tag can be narrowed by using the radiation pattern 31 obtained by combining the first and second element antennas 2a and 2b in the same phase and the radiation pattern 32 of the first element antenna. it can. FIG. 16 is a radiation pattern diagram of the antenna unit 2 according to Embodiment 2 of the present invention. FIG. 17 is a flowchart showing the operation of the bolt loosening detection apparatus according to the second embodiment of the present invention, and shows details of the ID information reading operation in step S10 shown in FIG.

  First, each switch of the antenna control unit 5 and the hybrid coupler 51 are switched by a control signal from the RFID reader / writer 3 to radiate radio waves with a radiation pattern 31 in which the first and second element antennas 2a and 2b are synthesized in the same phase. Then (step S11), the response wave from the RFID tag is demodulated to obtain ID information (step S12). Here, ID information of the RFID tags 11a and 11b existing in the region of the radiation pattern 31 is acquired.

  Next, each switch of the antenna control unit 5 and the hybrid coupler 51 are switched by the control signal from the RFID reader / writer 3 to radiate radio waves with the radiation pattern 32 of the first element antenna 2a alone (step S16), and the RFID tag ID information is acquired by demodulating the response wave from (step S17). Here, ID information of the RFID tags 11a and 11c existing in the region of the radiation pattern 32 is acquired.

  The RFID tag included in the detection area 35 (shaded portion shown in FIG. 16), which is the common reading range of the radiation pattern 31 and the radiation pattern 32, is recognized as an identification target, and the ID information is read (step S18). The detection area 35 is a common part of the radiation pattern 31 and the radiation pattern 32, and is a narrower area than the radiation pattern 31. Here, the RFID tag 11a existing in the area of the radiation pattern 31 and existing in the area of the radiation pattern 2 is the identification target.

  The detection area is not limited to the hatched portion shown in FIGS. The common area of the first radiation pattern and the second radiation pattern, or the area belonging to only one of the radiation patterns is set as a detection area, and the ID information acquired in the detection area is the ID of the RFID tag 11 to be identified. Read as information. As the first and second radiation patterns, the radiation pattern 31, the radiation pattern 33, the radiation pattern 32 of the first element antenna, and the radiation pattern of the second element antenna are combined to generate a detection area suitable for the system. it can.

  In the second embodiment, the case where the antenna unit 2 is configured by the two element antennas 2a and 2b has been exemplarily described. However, the number of element antennas is not limited to this. For example, the antenna unit 2 may be configured by a phased array antenna having n element antennas, and the antenna control unit 5 may perform beam control of the phased array antenna.

  In the bolt loosening detection system according to the second embodiment, the antenna control unit performs beam control of the antenna unit, thereby narrowing the beam width of the antenna unit and narrowing the detection area for reading the RFID tag. In addition, the radiation pattern of the antenna unit can be switched, and the detection area can be narrowed using a plurality of radiation patterns. By narrowing the detection area, it is possible to accurately detect only the ID information of the RFID tag to be identified, and prevent erroneous detection of ID information of the RFID tag located in the vicinity. Thereby, even in a system in which the relative speed between the bolt management tool and the bolt loosening detection device is large, it is possible to accurately detect the bolt loosening.

DESCRIPTION OF SYMBOLS 1 Bolt loosening detection apparatus 2 Antenna part 2a 1st element antenna 2b 2nd element antenna 3 RFID reader / writer 4 Detection part 5 Antenna control part 10 Bolt management tool 11 RFID tag 12 Radio wave shielding cover 13 Slit 20 Bolt 31 Radiation pattern 32 Radiation pattern 33 Radiation pattern

Claims (7)

An RFID tag fixed to the bolt;
A radio wave shielding cover provided with a slit and covering the bolt and the RFID tag;
A bolt management tool having
An antenna unit that receives radio waves radiated from the RFID tag and passed through the slit;
An RFID reader / writer that demodulates radio waves received by the antenna unit and reads ID information of the RFID tag;
Based on whether or not the ID information of the RFID tag can be read, a detection unit that detects looseness of the bolt;
A bolt looseness detecting device having:
Bolt loosening detection system equipped with.   The bolt loosening detection system according to claim 1, wherein loosening of the bolt is detected based on a received electric field intensity of a radio wave radiated from the RFID tag.   The loosening of the bolt is detected when the difference between the received electric field intensity of the radio wave radiated from the RFID tag and the received electric field intensity previously acquired for the same ID information is larger than a predetermined determination value. The bolt loosening detection system according to claim 2. The antenna unit has a plurality of element antennas,
The bolt looseness detection device includes an antenna control unit that performs beam control of the antenna unit,
ID information acquired when the antenna control unit causes the antenna unit to form the first radiation pattern, and acquired when the antenna control unit causes the antenna unit to form the second radiation pattern. The ID information acquired only by the common ID information or only one of the radiation patterns among the ID information is read as the ID information of the RFID tag to be identified. The bolt loosening detection system according to any one of the preceding claims. The bolt is a fixture for fixing a rail for railroad to sleepers,
The bolt looseness detection system according to any one of claims 1 to 4, wherein the bolt looseness detection device is installed in a train traveling on the rail for rail. An antenna unit that receives radio waves radiated from an RFID tag covered by a radio wave shielding cover having a slit and passed through the slit;
An RFID reader / writer that demodulates radio waves received by the antenna unit and reads ID information of the RFID tag;
Based on whether or not the ID information of the RFID tag can be read, a detection unit that detects looseness of the bolt;
Bolt loosening detection device comprising: An RFID tag fixed to the bolt;
A radio wave shielding cover provided with a slit and covering the bolt and the RFID tag;
Bolt management tool with

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